We live in a world that requires a lot of electricity. But few people realize the wasteful process it takes from AC mains to actual load. For a large computer data center with 500 kW requirement, additional 335 kW are lost between the AC mains to the CPU and core logic on the PC board. The 480V AC to 208V AC transformer is 99% efficient. The AC Uninterruptible Power Supply (UPS) is 92% efficient. Distribution of AC power is 99% efficient. Commercial grade AC-DC 12V power supply is 75% efficient, and finally the conversion efficiency from DC 12V to 1V is 88% efficient. When the power is coming from the back up batteries of the UPS, the battery charger loses another 10% efficiency. It is clear that 1% efficiency increase through the power conversion process has significant impact across the entire nation. The crux of the problem is the same for all power conversion systems: The power conversion system capacity is too large for most practical loads, therefore their operation is inefficient and not optimized. When load requirement drops, the power conversion system is not adaptive, and loses even more in efficiency. Rather than tackle the entire power conversion chain, we will focus in detail on how the present invention works for an AC to DC battery charging system. Later on, explanation on present invention to DC to DC battery charging system and DC to AC inverter will be given. It would be obvious then that adaptive power conversion system works for all power conversion systems with known characteristic loads.
The demand for automobiles with electric propulsion is increasing due to the diminishing oil supply and concerns on Carbon emission to the atmosphere. A typical electric car today has a battery capacity of 22-50 Kilo-Watt-Hour (KWh). The battery packs can be charged by regeneration of brake energy, charged by burning gasoline, or preferably charged from the nation's electric grid via an AC to DC power supply or indirectly, DC to DC power supply. When a large fleet of electric cars are in operation, the energy transfer efficiency of the electric car battery charger can make a big difference in energy requirement. For example, a one-percent difference in battery charger energy transfer efficiency for a fleet of 100,000 cars, each having 32 KWh capacity, is 32 MWh for each charging operation, not a small demand when compared with a small coal-fired power plant of a 50 MW power generating capacity.
However, prior art battery charger can only manage energy transfer efficiency close to 90%, even with the latest resonant converter power supply technology. It is desirable to have a battery charging system with significantly better energy transfer efficiency. It is desirable to have a battery charging system that is both high efficient and high reliability. It is also desirable to have a battery charging system that is inherently redundant with graceful degradation. It is also highly desirable to have a battery charging system that can charge more than one battery pack at the same time.